Sensitive detectors of electromagnetic radiation constitute an area that has been much studied but that encompasses many challenges. Production and detection of single photons in the microwave frequencies is a technical field that has proven to be challenging. In the prior art, sensitive detectors have been constructed for electromagnetic radiation particularly in the optical frequency range, whereby the frequency of radiation is at least tens of terahertz. Such photodetectors, i.e. sensitive detectors, of the optical range can be implemented by various techniques, such as by photodiodes or by the CCD technology, but it has been essential of the operating environment for the detectors of the optical range that the photons carrying radiation are photons propagating in a free space.
In the area of microwave radiation, publication Romero et al.: “Photodetection of propagating quantum microwaves in circuit QED, Phys. Scr. T137 014004, published on 14 Dec. 2009” has been disclosed in the prior art. Romero discloses a detector, i.e. a photodetector, operating in a metallic micro-waveguide in such a way that small absorber pieces are disposed to the waveguide either as a group or at equal intervals. The principle in Romero is that, as a microwave photon hits the pieces in the waveguide and absorbs therein, coherent excitations occur, causing changes in the absorber states. Romero specifically detects these changes of state. The greatest problem in Romero is that it requires a large number of absorbers that must be accurately measured one by one. The detector therefore becomes large and complicated to use. In addition, the photons can scatter from the absorbers without being absorbed which increases the detector error.
In general, the main problem of the prior art is that, in entering the microwave range, i.e. in calculating the frequency from the order of terahertz up to 10 GHz, it has not been possible to produce an accurate photon detector that would accurately detect even single photons and thereby enable quantum calculation in the microwave range. In other words, there exists a fundamental demand for an extremely sensitively operating detector of microwave photons, in view of the development of the state of the art technology, such as even a quantum computer.